Field of the Invention
The present invention relates to an inkjet printing apparatus and a preliminary discharging method, and particularly, to control of preliminary discharge for keeping a satisfactory discharge state of a print head, such as control of the number of times of the discharge during preliminary discharge.
Description of the Related Art
As an example of preliminary discharge, there is known an aging process which is performed in order to avoid a change in density among nozzles caused by the influence of a burnt deposit occurring inside a nozzle of a print head. As for the aging process disclosed in Japanese Patent Laid-Open No. H08-039825(1996), the cumulative number of times of the discharge for each nozzle is obtained and the number of times of the discharge for each nozzle during preliminary discharge is set according to the cumulative number of times of the discharge. More specifically, the number of times of the discharge is set so that the number of times of the discharge during the preliminary discharge is greater in the nozzle of which the cumulative number of times of the discharge is smaller. Thereby, it is possible to suppress an increase in the amount of the ink consumed in the entire print head during the aging process.
However, in Japanese Patent Laid-Open No. H08-039825(1996), the number of times of the discharge for the aging process is set for each nozzle based on the cumulative number of times of the discharge of each individual nozzle. For this reason, the number of times of the discharge during the aging process, that is, the time necessary for the preliminary discharge varies among the nozzles. Thus, there is a case in which the time necessary for the preliminary discharge may be comparatively long in a particular nozzle. In such a case, in the nozzle of which the discharge time is comparatively short, for example, ink mist caused by a printing operation before the preliminary discharge is thickly attached to the nozzle during the preliminary discharge. As a result, there is a concern that the subsequent discharge may be influenced. On the contrary, a method may be supposed which removes the mist by wiping a surface where the nozzles are arranged (a nozzle arrangement surface) in the print head before the preliminary discharge. However, when the wiping operation is performed with no exception before the preliminary discharge, there is also a concern that the throughput of the apparatus may be degraded.
Depending on the time taken for the preliminary discharge, the amount of the ink mist generated by the preliminary discharge may eventually influence the other parts of the printing apparatus. On the contrary, the preliminary discharge can be performed while the nozzle arrangement surface of the print head is covered by a cap. However, in such a configuration, since the print head is covered by the cap even when the amount of the generated ink mist does not influence the other parts, the throughput is decreased due to the capping operation.